1. Field of the Invention
The present invention relates to an improvement of a windmill type electrode for use in a vacuum switch tube.
2. Description of the Prior Art
A conventional vacuum circuit breaker is constructed such that an electrode provided therein is formed with grooves to control an electric current flowing in the electrode and form an alternate loop-like electric way in a substantially circumferential direction, whereby an arc current generated in the electrode is activated in accordance with the magnetic field produced by the loop-like electric way, so that a partial dissolution of the electrode can be avoided and thus the breaking function thereof as a whole can be greatly improved thereby.
FIGS. 8 and 9 are illustrations each showing a windmill type electrode disposed in a vacuum switch tube as conventionally disclosed by Japanese Patent Publication No. 56-36774. In the figures, reference number 1 denotes a pair of electrode bars disposed inside the vacuum tube (not shown); one of which is a fixed electrode bar and the other is a perpendicularly movable electrode bar which is located right beneath the fixed electrode bar opposing thereto, wherein a detachable windmill type electrode 2 is mounted at the end portion of each of these electrode bars in such a manner that two windmill type electrodes are facing respectively to each other.
The windmill type electrode 2 is provided with a plurality of arc current passing surfaces 20, 20A and 20B formed in the external periphery thereof which are to be brought into contact with the other electrode opposing thereto, and also provided with a plurality of grooves 21, 21A and 21B which are placed therein in such a form as to extend from the external side towards the inner side of the electrode, wherein the center portion thereof is formed in a dented shape. By the way, the grooves 21, 21A and 21B respectively comprise a portion that contacts with an inner circle of the corresponding arc passing surface 20, 20A and 20B, and a portion which is in parallel with the groove adjacent to the arcuate portion of the inner circle. In FIG. 8, the points A, E, G and H of the arc current passing surfaces 20, 20A and 20B respectively indicate the points in which the arc current 3 is generated in the respective arc current passing surfaces.
With the above construction, when the electrodes 2 in FIG. 9 are opened, an arc current 3 is generated on one of the arc current passing surface 20, 20A or 20B. The arc current generated at one of the points A, E or G of the respective arc current passing surfaces 20, 20A and 20B receives a magnetic activating force produced by the effect of the current flowing path of the electric current I made in accordance with the grooves 21, 21A and 21B, and moves along the circumferential direction F as shown in FIG. 8. Thereafter, the arc current 3 continues to receive the magnetic activating force even after it reaches to the groove 21, 21A or 21B, and thereby passes over the groove to the adjacent arc current passing surface to rotate around.
In addition to the reference mentioned above, other references that disclose this type of conventional vacuum circuit breaker are Japanese Patent Application Laid Open No. 2-142024, 62-31917, 58-100325, Japanese UM Reg. Application No. 55-91024, 58-173145, 61-197627, 62-64939 and Japanese Patent Application Laid Open No. 2-86021 as the prior arts of this type apart from the above mentioned prior art.
However, since the conventional vacuum switch tube is constructed as above and the electrode 2 is formed with a plurality of delved grooves 21, 21A and 21B, the time required for the arc current to pass over these grooves varies and sometimes the movement thereof stands still. Also, if the point at which the arc current is generated is H in the arc current passing surface 21A as shown in FIG. 8, a magnetic activating force to activate the arc current 3 by way of the path of the electric current I is applied to the direction in which the arc current is pushed towards outside the circle, and for this reason the arc current 3 can not smoothly rotate on the arc current passing surfaces 20, 20A and 20B.